Steel rule die stripping device



Feb. 2, 1965 J. B. MADSEN 3,167,985

STEEL RULE DIE STRIPPING DEVICE Filed May 24. 1961 INV EN TOR.

ATTORNEY United States Patent Office 3,ib7,985 Patented Feb. 2, 1965 3,1161% STEEL RULE DEE STRIPPING DEVIrCE James Eagle Madscn, London, Ontario, Canada, assignor to General Motors (Iorporation, Detroit, Mich, a corporation of Delaware Filed May 24, I961, Ser. No. 112,339 1 Claim. (Cl. 83--l39) This invention relates to steel rule die type punch and die assemblies for punching blanks of predetermined configuration from sheet stock.

The invention is particularly related to new and improved stripping devices for use with punch and die assemblies. In the prior art, it has been proposed to utilize rubber strippers, positioned adjacent the steel cutting blades, which will be compressed during the punching operation by the stock so that, when the punching pressure is relieved, the stock will be stripped clear of the punch and the die. Examples of previous stripping devices are shown in U.S. 2,850,096 and in U.S. 2,899,849. In order for rubber strippers to be effective, the outer surfaces thereof must be exactly positioned relative to the cutting edges of the punch and the die so that the parts punched from sheet stock and the surrounding stock will be faced clear of the punch and the die after the punching operation. Furthermore, the compressibility of the material must be exactly calculated so that the rubber will be sufficiently compressed within the die to prevent interference with the punching operation. For example, if the compressed position of the rubber stock is not located inwardly a suflicient distance to permit the parts being punched to be freely displaced within the die cavity, the metal will be unevenly sheared and an unsatisfactory punched part will result.

It is an object of this invention to provide a new and improved rubber stripper design. Another object of this invention is to provide a rubber stripping design which accommodates the compressive and expansive characteristics of the strippers to prevent interference with a punching operation. Still another object of this invention is to provide a new and improved rubber stripper design which strips metal parts from steel rule die sets in a more efficient manner. Other objects and advantages of this invention will be apparent by reference to the following detailed description and the accompanying drawing wherein:

FIGURE 1 is a partial sectional view of steel rule die apparatus embodying the present invention;

FIGURE 2 is a partial cross sectional view of the apparatus illustrated in FIGURE 1 in another position; and

FIGURE 3 is a perspective view of steel rule apparatus embodying the present invention.

Referring now to the drawing, a steel rule die set comprising an upper platen it) and a lower platen 12 is illustrated. A punch plate 14 having the contour of a part to be fabricated is secured to the lower platen 12 and a corresponding female die is formed on the upper platen by a plurality of steel blades 16 in a conventional manner. Plywood spacer blocks 18, 20 abut the steel blades 16 and the outer surfaces 22, 24 thereof are spaced from the outer surface 26 of the steel blades to define a punch cavity.

Lengths of rubber strippers 28, 3% are spaced around the inner periphery of the steel blades within the punch cavity and around the outer periphery of the punch plate 14. The strippers are made from suitable rubber stock such as 75 Durometer neoprene sheet or the like. The strippers may be made solid or may be laminated as illustrated. The advantage in providing laminated rubber strippers is that the desired height of the strippers can be more easily controlled so that the bottom surface 36 of the rubber stripper 28 and the upper surface 38 of the rubber stripper 30 can be exactly positioned relative to the lower surface of the steel blades and the upper surface 40 of the punch 14.

The strippers are secured to the adjacent support surfaces 32, 34 by cementing with a suitable conventional adhesive. To eliminate the serious problems encountered when insufiicient room is provided for the expansion of the rubber strippers during the cutting operation, a rubber stripper having a novel corrugated design is utilized as shown in FIGURE 3. The sections of the rubber stripper are provided with oppositely directed V-shaped grooves 42, 44 having side surfaces which intersect at approximately 60. Although other corrugated or sinuous designs could be utilized, I have found that equal opposite 60 corrugations provide uniformly good results in use.

In operation A workpiece 46 of sheet metal is positioned between the dies as shown in FIGURE 1. The steel blades 16 are then forced downwardly through the sheet metal as shown in FIGURE 2. Downward movement of the steel blades 16 causes compression of the rubber stripper elements 28, 3t) and, consequently, longitudinal and transverse expansion thereof. When the platen 10 is moved upwardly after the shearing operation, the rubber strippers will expand upwardly and strip the severed workpiece from the cavity defined by the steel cutting blades 16. The dimensional arrangement of the lower surface 36 of the stripper 28 relative to the lower surface 26 of the steel cutting blades is critical, in that, the bottom surface 36 must project a sufficient distance outwardly beyond the surface 26 in the open position of the dies so that a severed piece of material will be completely removed from the cavity defined by the blades. If the surface 36 does not extend outwardly a sufficient distance, the severed pieces of the sheet metal 46 will tend to stick within the cavity. On the other hand, the distance that the bottom surface 36 can project outwardly is also limited, in that, there must be sufficient room provided within the cavity defined by the blades after the completion of the severing operation to allow for expansion of the rubber stripper. When solid rubber stripper elements are used as disclosed in U.S. 2,850,096 and U.S. 2,899,849, it is extremely difiicult to obtain precisely the right spatial relationship between the surfaces 26, 36 due to the fact that solid rubber strippers are not as freely expandable as a corrugated rubber stripper. The corrugated rubber stripper permits expansion, not only transversely of the rubber elements, but also longitudinally thereof and across smaller areas of rubber. The V-shaped grooves which extend transversely of the rubber elements permit expansion thereof in a manner which greatly facilitates the stripping function and permits the surface 36 to be located outwardly of the surface 26 a greater distance than with conventional solid strips of rubber. Since the corrugated rubber stripping elements have a far greater ability to expand in the compressed state, the spatial relationship between the surfaces 26, 35 does not have to be as critically maintained as in previous practice and a greater width of rubber can be extended outwardly beyond the surface 26 in the open position.

An unexpected result of the improved design is an improvement in the wearing qualities of the rubber stripper elements. The improvement in wearing qualities is apparently explained by the fact that a greater amount of rubber may be provided outwardly of the surface 26 and, hence, although the wear rate of the rubber along the surface 36 may be substantially equivalent, a greater amount of rubber is available to be worn away. In any event, the "rubber stripperslast a longer time Without replacement than in previous practice, where the spatial relationship of the surface 36 relative to the surface 26 had to be extremely closely controlled to the extent that small amounts of Wear of the surface 36 often reduced the spatial relationship to the point where solid rubber strippers no longer functioned properly.

Another advantage of this invention is the provision of laminated rubber strips. In this manner, the outer portions of the rubber strippers can be replaced when necessary with a consequent saving in material. The laminations may be readily cemented to one another, and since the spatial relationship of the outer surface 36 is not critical relative to the surface 26, the addition of another lamination may be made quickly and without precise calculation. When an outer lamination is added to a Worn corrugated rubber stripper element, the replacement may be fitted so that a substantial portion of the. surface 36 extends beyond the surface 26 in the open position without closely controlling the distance.

Obvious modifications and changes in the arrangement of the parts are intended to be included within the scope of this invention as defined by the appended claim.-

The invention claimed is: I

In a die set for blanking out a shape from sheet metal; a shaped male punch member, a female die member, means mounting said punch member and said female die member in mutufl alignment for relative movement tointo an engaged position, said female die member comprising die blade means defining an opening of predetermined contour, said punch member adapted to fit within said opening, rubber stripper means located adjacent the peripheries of said die blade means and punch member, said stripper means adjacent said punch member spaced from said punch member to provide a working space for said die blade means, said stripper means formed of flat elongated strips of rubber laminated together to form a built-up member being of a depth greater than said die blade means when in the spaced position and having corrugation formed along the opposite edges side thereof, said corrugations greatly increasing the exposed surface of said stripper means and permitting greater axial and transverse expansion thereof when said punch member and female die member are in the engaged position, the exact spacial relationship of the outer surface of the rubber stripper means therefore not being critical relative to the outer surface of said die blade means due to the softer spring rate of the stripper means.

References Cited in the file of this patent UNITED STATES PATENTS 422,576 Eager Mar. 4, 1890 2,494,018 Urquhart Jan. 10, 1950 2,553,615 Wales May 22, 1951 2,807,323 Taylor Sept. 24, 1957 3,048,069 Berlin et a1. Aug. '7, 1962 

